Regulation of vane pumps

ABSTRACT

A regulatable vane pump is provided with a piston operable by differential pressure responsive to booster steering flow demand wherein the piston movement controls a choke bore flow area. The differential pressure is effected by pump pressure on one face of the piston and consumer pressure on the opposite face of the piston, e.g., pressure in a booster steering servomotor. The choke bore has an aperture covered or uncovered by a choke plate carried by a pin on the piston. The choke plate is normally in position so as not to impede flow through the choke and the piston is in a position such that pump outlet flow is blocked from a bypass passage back to the pump inlet. However, with rise in vehicle speed under non-steering conditions, causing pressure on the one face of the piston to shift it along with the choke plate, the choke bore is closed, or partially so, and the unnecessary output pressure flow shunted back to pump inlet. Under steering conditions the back pressure on the opposite face of the piston reverses the piston to open the choke bore, all dependent on vehicle speed and rapidity of the steering operation.

BACKGROUND OF THE INVENTION

Vane pumps, in particular, are used very frequently for supplyingauxiliary power steering mechanisms with pressure oil. Narrowing thepressure channel at an output flow point is a known way of controllingthe stream of oil being delivered for the auxiliary power steeringmechanism. This method causes a higher velocity of flow, andconsequently a reduction of the static pressure on the booster piston orconsumer end of the flow-regulating piston. Thus, the differentialpressure between the flow regulating-piston end surfaces become greaterand the flow-regulating piston is caused to shift responsive to the rateof pump speed, which is dependent on engine speed and thus correspondsto vehicle speed. Consequently, the flow admission port into the bypassor return channel for oil flow from pump outlet to inlet, or suctionside, is opened to a corresponding extent. Accordingly, more hydraulicfluid is recirculated in the pump and the flow of oil to the consumerdecreases. A dropping or falling characteristic curve of the vane pumpoccurs, i.e., the pump discharge is not increased with the work done bythe vane pump after a certain cutoff point is reached, but is evenreduced, if desired.

Certain characteristic curve variants are desired for various reasons.Thus, or example, a falling characteristic curve provides bettersteering operation in an auxiliary power steering mechanism at highspeeds. Furthermore, the booster pressure in the steering systemdecreases when the characteristic curve of the flow of oil is falling ifthe speed is increasing. The result is a smaller consumption of power bythe pump, and that effects lower temperatures.

For energy saving reasons and to avoid high oil temperatures, it isdesirable to have small oil volume flowing through the booster system,especially when driving on a high-speed straight stretch of road. On theother hand, a high flow of oil should be available for a steeringoperation when operating pressure is high.

A known device for regulating vane pump is disclosed in applicant'sGerman Patent No. DE-OS No. 32 11 948, the U.S. counterpart being U.S.Pat. No. 4,536,133 issued Aug. 20, 1985 to applicant. In that patent aleaf spring is fastened to the front of the flow-regulating piston tocontrol flow through choke bores 14,15. During the movement of theflow-regulating piston, the free end of the leaf spring effects reducedflow through the choke bore(s). Thus, a decreasing characterisic curveof the flow of oil is obtained through the entire speed range after acertain speed cutoff point (28 on FIG. 8 of U.S. Pat. No. 4,536,133) isreached. Consequently, a predetermined characteristic curve pattern canbe effected.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

The present invention provides greater variation in the characteristiccurve pattern.

A choke member having a choke bore is disposed so that a choke platecarried by the flow-regulating piston can slide across the choke bore torestrict flow to the bypass channel responsive to speed. By suchconstruction, numerous characteristic curve variants can be achieved byshaping the leading edge of the choke plate, e.g., linear, curved, etc.Thus, a varied selection of choke plates may be used. Such arrangementis very simple and safe. The movement of the choke plate is parallel tothe movement of the flow-regulating piston and no leaf spring isrequired. Accordingly, there is no danger of a fatigue fracture, e.g.,of the leaf spring. Furthermore, the regulator piston with the chokeplate can be produced easily at a favorable price.

In the embodiment of the invention the choke member is a tube parallelto the flow-regulating piston and the choke bore is located in acircumferential wall of the tube.

A space-saving arrangement is achieved in that the choke plate need notconnect at the extended front of the regulator piston, as required for abendable leaf spring which also has to be rigidly attached to theregulator piston. The choke plate of the invention can be installed orremoved easily. Accordingly, choke plates can be readily changed to makechanges in the characteristic curves of steering operation at any time.

Thus, regulating devices can be manufactured in production and assembledto conform to selected requirements for choke plate selection.

The choke tube member and choke plate can be contiguously cylindrical inshape for simple production and accurate throttling coaction.

The choke plate and tubular choke member can be designed with largetolerances since the choke plate can be held against the circumferencialwall of the choke tube by a spring in ways to be described. Also,different distances between the choke plate and piston are usable.

Thus, a spring makes installation easier. Further, the choke tube canabut the cheek or pressure plate of the pump pressure chamber to makeinstallation easier while making sure that the choke plate is heldagainst the choke tube member. Accordingly, additional safety measureare rendered unnecessary.

If the choke bore be offset on the circumference of the choke tube withrespect to the choke plate, additional characteristics can be effected.For example, a lateral edge of the choke bore can become a leading edgeand the choke bore or bores can be given any desired shapes. Likewise,the choke plate, in conformity with the choke bore, can have any desiredshape for variations of closure coaction with a choke bore or bores ofvarying shape to achieve a variety of regulatory characteristics.

A very advantageous feature of the invention is the provision of asimple bore, e.g., of a circular cross section in the choke tube, inaddition to the choke bore, for separate passage of pump discharge to aconsumer for improvement in cold-starting of a vehicle's steeringmechanism.

For ease of installation, the regulating piston can be provided with atransverse slidably keyed pin which carries the choke plate against thechoke tube. This also permits ease of disassembly.

Other advantages and features of the invention will be apparent from thedetailed description to follow in conjunction with the appended drawing,in which:

FIG. 1 shows a longitudinal section through a vane pump with theflow-regulating piston components of the invention in the closedposition to prevent bypass of pump output to inlet.

FIG. 2 shows a longitudinal section corresponding to that shown in FIG.1, but with the flow-regulating piston shifted to permit bypass flow.

FIG. 3 is a section on the line III-III of FIG. 2.

FIGS. 4 through 8 show various possible shapes of choke plates, as seenin profile, FIG. 6 being preferred.

FIG. 9 shows a modified flow-regulating piston corresponding to FIG. 2,but on a small scale and having a regulating piston carrying a chokeplate which is longitudinally adjustable by means of a threaded screw.

The vane pump's construction is essentially conventional. Only thoseparts that are essential to illustrate the invention are represented indetail in the drawing.

Thus, the pump will be understood to have a rotor with blades, in theusual manner, and being located between a front plate (not shown) at thefront and a rear pressure plate 1 (FIG. 1). Behind the pressure plate 1,there is a pressure chamber 24 understood to be connected for flow frompressure cavities (not shown) by pressure passages (not shown).

Output pressure passes through a tubular choke member 2 to a pressureoutput port 3, from which a passage can lead to a consumer, for example,an auxiliary power steering mechanism.

The choke member 2 is in the form of a tube or cylinder as shown. Achoke bore 4 and additional bore 5 are through the circumferential wall.Communication from the outlet pressure chamber 24 to the port 3 isthrough the bores 4 and 5, with the choke member 2 being provided with alongitudinal bore 6 for that purpose.

The front end of a flow-regulating piston 7 projects into the pressurechamber 24, and abuts the outer side of the pressure plate 1 as a limitstop. The flow-regulating piston 7 is located slidably shiftable in abore in the housing or the cover of the vane pump. The rear surface ofthe flow-regulating piston 7 is exposed in a spring chamber 8 in which aspring 9 exerts a bias force on the flow-regulating piston in thedirection of the pressure plate to prevent bypass flow. The chamber 8 isconnected with a pressure chamber 11 through a transverse bore 10,pressure chamber 11 being located adjacent the choke member 2 to receivepump output pressure.

The flow-regulating piston 7 is provided with a leading edge 12 whichcoacts with admission port 13 for flow to return or bypass conduit 14for return of pump output to the inlet or suction side of the pump.

The tubular choke member 2 and the flow-regulating piston 7 are parallelto each other. The admission port of the choke bore 4 is axiallytransverse, i.e., perpendicular to the longitudinal axis of theflow-regulating piston 7. A flow restrictor means 15 consists of a chokeplate 16 and a pin 17. The pin 17 is located in a transverse bore 18 inthe flow-regulating piston 7. The transverse bore 18 is a blind-holebore and a spring 19 is compressed between the bottom of the blindholebore 18 and the rear end of the pin 17. Thus, the choke plate is alwayspressed against the circumferential wall of the choke member 2.

As can be seen from FIG. 3, the choke plate 16 has the shape of asegment of a hollow cylinder whose internal diameter at leastapproximately conforms to the external diameter of the tubular chokemember to provide good sealing and throttling effect. Furthermore, therestrictor means 15 also comprises a protective device against twistingon the flow-regulating piston by slidably keying in the blind bore andit can be manufactured easily and at a favorable price as a die castingor injection molding. Various materials, including plastics, are usable.

Instead of the one choke bore 4 that is shown, several choke bores canbe located in tandem longitudinally or around the circumference in thechoke member 2, if desired. When that is done, choke bores can also beoffset around the circumference with respect to the choke plate 16. Inthis way, a partial masking and consequently also a certain independenceof the regulating piston's stroke becomes possible, if desired.

In FIG. 3, a pressure cavity 20 through which the pressure chamber 24 issupplied with pressure oil is indicated with broken lines.

As can be seen in FIGS. 1 and 2, the front end of the cylindrical chokemember 2 that projects into the pressure chamber 24 has a radial flange21 that abuts the pressure plate 16 on one side and limits the axialmovement of choke plate 16 under bias of spring 9. Furthermore, the pin17 of the restrictor means 15 can be provided with a keyway 22 tomaintain axial alignment.

Thus, easy starting of installation and disassembly is provided.

Various embodiments of the choke plate 16 are shown in plan view inFIGS. 4 through 8. In addition to a simple rectangular shape, as isshown in FIGS. 1 through 3, shapes can be selected in which the frontedge 23, in particular, is something other than a straight line. In thisway, the possibilities of variation where characteristic curve patternsare concerned become even greater. Furthermore, additional changes inoperation by using a modified choke plate 16 can be done easily.

Characteristic curves that have reduced dropping off are obtained at thebeginning of the area of overlapping with the embodiments shown in FIGS.4 through 6. Especially with an embodiment as shown in FIG. 6, concavelysemicircular at the front edge 23, a partial straightening of thecharacteristic curve is obtained since the choke bore 4 is morerestrictively closed at the beginning of traverse.

An opposite effect is obtained with an embodiment such as is shown inFIG. 7. In that case, the characteristic curve pattern can even riseslightly after the cutoff point is reached.

FIG. 8 shows a front edge 23 with an inclined edge.

The examples shown in FIGS. 4 through 8 are to be regarded as only apart of a large number of possibilities. Depending upon the use to whichthey are to be put in each case and upon the desired chracteristic curvepattern, a number of possible variations are presented here.

The operation of the invention functions is as follows:

When the vane pump starts up, and up to a cutoff point with increasingspeed, the flow-regulating piston 7 is in the closed position shown inFIG. 1. The pressure chamber 24 is not connected with the bypassadmission port 13 to the return conduit 14 for the flow of oil to thepump inlet because of the closed position of the leading edge 12 of theflow-regulating piston 7. The pressure medium coming out of the presurecavities generally flows through the constant area bore 5 and the chokebore 4 into the choke member 2, and from there through the centrallongitudinal bore 6 to the outlet port 3. There is an appropriatepressure difference between the pressure chamber 24 and the springchamber 8. Up to the cutoff point, the volume flowing through increasescorrespondingly as the pump speed increases. The piston 7 goes throughan opening movement after the cutoff point is passed which point isdetermined by flow through the bores 4 and 5. A connection between thepressure chamber 2 and the return conduit 14 is produced in that way andthe surplus pressure medium can flow out of the two pressure cavities inappropriate quantities and be returned to the suction side of the pump.

However, as a result of the flow-regulating piston's opening movement,the restrictor means 15 approaches the choke bore 4 with the choke plate16. If the flow-regulating piston now is moved further, the choke plate16 increasingly moves edgewise over the choke bore 4. In this way, agradual throttling is achieved.

Now, as soon as the hydraulic steering mechanism is activated, theflow-regulating piston 7 goes through a reverse, closing, movementbecause of the back pressure from the consumer into the spring chamber8. This, in turn, results in a complete or partial opening of the chokebore 4. In this way, a greater quantity of oil is made available to makecertain of adequate speed of steering, particularly when steering in theupper speed range. At high rates of speed on long straight roadstretches, only a small flow-through of volume takes place. But, ifsteering is to take place at this high rate of speed, wherein theoperating pressure increases accordingly, the volume flowing through,i.e., oil circulation, increases correspondingly and with increasingpressure. As a result, a volume flow sufficient for steering is alwaysavailable.

The bore 5 serves the purpose of improving cold-starting steeringperformance. In this case, in fact, it only functions in the openposition and the danger of cavitation is reduced because of the smallquantity flowing through.

A transverse bore that passes through the end of regulating piston 7 canbe used instead of a blind-hole bore 18, if desired. In this waysymmetry is obtained and no mistakes in installation can occur. In thisembodiment, the spring 19 is then located between the bottom of thechoke plate 16 and the circumferential wall of the flow-regulatingpiston 7 around the pin 17.

The dimensions of the longitudinal bore 6 in the choke member can besuch that it determines the cutoff point. For this purpose, it is onlynecessary that the flow-through cross sections of the choke bore 4 andthe bore 5, together, should be larger than the flow-through crosssection of the longitudinal bore 6.

In addition to an improvement of cold-starting performance by the bore5, that bore can also serve the purpose of influencing thecharacteristics of the characteristic curve. The dropping tendency ofthe characteristic curves can be influenced by it, depending upon boresize.

In FIG. 9, on a reduced scale, the front area of a flowregulating piston7 is shown in which the pin 17 of the servopiston 15 is not inserteddirectly in a transverse bore 18 of the flow-regulating piston 7.Instead, the lower part of the servopiston 15 has a base part 25 with athreaded screw 26. There the pin 17 is also inserted in a transversebore of the base support 25 or it and the base support 25 can constitutea single piece. In this case, the front face of the flow-regulatingpiston 7 has a threaded bore into which the threaded screw 26 of therestrictor means 15 can be screwed. The advantage of this embodiment bycomparison with the embodiments that have been discussed is in the factthat the distance "x" is adjustable and can even be changedsubsequently, if desired. That means that changes in the characteristiccurves are possible in this way, and as a result the device of theinvention can be adapted to the existing circumstances in the best waypossible. It is only necessary that securing of the threaded screw 26 inits adjusted position is made after a final adjustment.

I claim:
 1. In a device for regulating the output of a vane pump of thekind wherein a pressure operated piston has one face exposed to outletpressure of a vane pump and an opposite face exposed to servomotorpressure wherein the position of the piston is responsive todifferential pressure on the piston faces, and including a bypasspassage wherein outlet pressure flow of the pump can return to the pumpinlet or be blocked therefrom dependent on piston position;theimprovement which comprises means (2) having a choke bore (4) and anoutlet passage (6) for pump flow to a consumer; said choke borecommunicating between said outlet passage and said one face of saidpiston exposed to pump outlet pressure and being axially perpendicularto the axis of said piston; a choke plate (16) carried by said piston tomove longitudinally therewith and disposed to slidably cross over saidchoke bore transversely of the axis thereof to closr or open said chokebore responsive to differential pressure on the faces of said piston. 2.In a device as set forth in claim 1, including means 26 for carryingsaid choke plate on said piston comprising a pin secured to said chokeplate and carried by said piston and having means (22) for aligning saidchoke plate.
 3. In a device as set forth in claim 2, including furthermeans for axially adjusting the position of said pin on said piston. 4.In a device as set forth in claim 1, including another bore (5) in saidchoke member communicating with said pressure chamber and said outletpassage to facilitate cold starting of a vehicle steering system.
 5. Ina device as set forth in claim 1, wherein said means (2) comprises achoke member (2) having a wall through which said choke bore extends tocommunicate said outlet passage with pressure to which said one face ofsaid piston is exposed.
 6. A device as set forth in claim 5 wherein saidchoke bore has an axis intersecting the axis of said piston.
 7. A deviceas set forth in claim 5 wherein said wall through which said choke borepasses is curved.
 8. A device as set forth in claim 7, wherein saidchoke plate is curved in conformity with said curved wall.
 9. In adevice as set forth in claim 8, including a spring biasing meanssupporting said choke plate in engagement with said curved wall.
 10. Ina device as set forth in claim 9, said spring biasing means comprises abore (18) in said piston, a pin (17) extending out of said bore andcarrying said choke plate and a spring (19) in said bore biasing saidrod to effect engagement of said choke plate with said wall.
 11. In adevice as set forth in claim 10, wherein said wall has curvature in thearea of opening of said choke bore across which said choke plate isslidable and said choke plate has complementary curvature.
 12. In adevice as set forth in claim 5, including a housing, said choke memberbeing carried in said housing and a vane pump pressure plate (1) abuttedby said choke member for fixing said member in said housing.
 13. In adevice as set forth in claim 12 said housing having a pressure chamber(24) for receiving pressure flow from said vane pump; said pressurechamber extending around said choke member for pressure flow throughsaid choke bore to said outlet passage (6).
 14. In a device as set forthin claim 13 wherein the choke bore is a slot.
 15. In a device as setforth in claim 13 wherein the choke plate has a straight edge movableacross said choke bore.
 16. In a device as set forth in claim 13 whereinsaid choke plate has a non-linear edge movable across said choke bore.17. In a device as set forth in claim 13 wherein said choke plate has astraight edge oriented to move broadside across said choke bore.
 18. Ina device as set forth in claim 13, wherein said choke plate has astraight edge oriented to move slantingly across said choke bore.